1. Field of the Invention
This invention relates generally to semiconductor-based vertical laser cavities (e.g., as used in VCSELs). More specifically, the top mirror of the laser cavity is non-planar, thus enhancing the performance of the laser cavity.
2. Description of the Related Art
As the result of continuous advances in technology, optical devices are becoming more important and more prevalent. For example, the increasing demand for communications bandwidth has resulted in an increased interest in optical communications systems, including those that transmit data over optical fibers. This, in turn, has resulted in increased demand for optical devices for use in these systems.
One general class of optical devices is those that are based on vertical laser cavities. In these devices, a laser cavity is formed by a bottom mirror and a top mirror and is oriented vertically with respect to a supporting substrate. In one common approach, different layers of material are epitaxially grown on the substrate to build up the vertical laser cavity one layer at a time. Pumping the active region within the laser cavity above its lasing threshold results in laser action. The laser action can be used for different purposes, depending on the design of the rest of the device. For example, in vertical cavity surface emitting lasers (VCSELs), the device is used as a source of laser light. The laser radiation generated by the laser cavity is output through one of the mirrors. In vertical lasing semiconductor optical amplifiers (VLSOAs), the device is used as an amplifier. The laser action within the vertical laser cavity gain clamps the active region. A second optical signal passing through the active region experiences amplification without significant gain saturation. For example, see U.S. patent application Ser. No. 10/014,679, “Integrated Optical Device including a Vertical Lasing Semiconductor Optical Amplifier,” by Jeffrey D. Walker and Sol P. Dijaili, filed Dec. 11, 2001, which is incorporated herein by reference. Other devices and uses exist for vertical laser cavities.
One drawback of vertical laser cavities is they can be difficult to fabricate and operate. Because of the geometry, the round trip laser path typically is not very long within the active region. This results in relatively low gain for each round trip. As a result, care typically must be taken to ensure that round trip losses are not too large. Otherwise, lasing cannot be achieved. The top and bottom mirrors are one significant component in determining the overall loss and performance of a vertical laser cavity. However, their design is often driven by fabrication limitations, resulting in less than optimal mirror designs.
Thus, there is a need for vertical laser cavities with improved mirror designs.